A conventional fixing device includes a heat roller and a heater. The heat roller is configured of a roller section having a thin-walled cylindrical shape and a coil wound along an inner circumferential surface of the cylindrical roller section. The thin-walled roller section results in a smaller heat capacity, thereby enabling the roller section to be heated promptly. Within the thin-walled roller section, the coil is wound more densely at an intermediate portion than at both end portions in order to reinforce the intermediate portion which tends to be weak in terms of strength.